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(#) Missing explicit orientation

!!! ERROR: Missing explicit orientation
   This is an error.

Id
:   `Orientation`
Summary
:   Missing explicit orientation
Severity
:   Error
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Resource files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/InefficientWeightDetector.java)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/InefficientWeightDetectorTest.java)
Copyright Year
:   2011

The default orientation of a `LinearLayout` is horizontal. It's pretty
easy to believe that the layout is vertical, add multiple children to
it, and wonder why only the first child is visible (when the subsequent
children are off screen to the right). This lint rule helps pinpoint
this issue by warning whenever a `LinearLayout` is used with an implicit
orientation and multiple children.

It also checks for empty LinearLayouts without an `orientation`
attribute that also defines an `id` attribute. This catches the
scenarios where children will be added to the `LinearLayout`
dynamically.

!!! Tip
   This lint check has an associated quickfix available in the IDE.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
res/layout/inefficient_weight.xml:3:Error: Wrong orientation? No
orientation specified, and the default is horizontal, yet this layout
has multiple children where at least one has layout_width="match_parent"
[Orientation]
&lt;LinearLayout
 ------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`res/layout/inefficient_weight.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers
&lt;?xml version="1.0" encoding="utf-8"?&gt;

&lt;LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"
    android:layout_height="match_parent"&gt;

	&lt;Button
	    android:layout_width="match_parent"
	    android:layout_height="wrap_content"
        android:layout_weight="1.0" /&gt;

	&lt;LinearLayout
	    xmlns:android="http://schemas.android.com/apk/res/android"

	    android:layout_width="match_parent"
	    android:layout_height="match_parent"

		android:orientation="vertical"&gt;

		&lt;Button
		    android:layout_width="match_parent"
		    android:layout_height="wrap_content"
		    android:layout_weight="1.0" /&gt;

	&lt;/LinearLayout&gt;

	&lt;LinearLayout
	    xmlns:android="http://schemas.android.com/apk/res/android"

	    android:layout_width="match_parent"
	    android:layout_height="match_parent"

		android:orientation="vertical"&gt;

		&lt;Button
		    android:layout_width="match_parent"
		    android:layout_height="0dip"
            android:layout_weight="1.0" /&gt;

	&lt;/LinearLayout&gt;

    &lt;LinearLayout
            xmlns:android="http://schemas.android.com/apk/res/android"
            style="@style/MyStyle"
            android:layout_width="match_parent"
            android:layout_height="match_parent"&gt;
        &lt;Button
                android:layout_width="match_parent"
                android:layout_height="wrap_content" /&gt;

        &lt;Button
                android:layout_width="match_parent"
                android:layout_height="wrap_content" /&gt;

    &lt;/LinearLayout&gt;


&lt;/LinearLayout&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/InefficientWeightDetectorTest.java)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `InefficientWeightDetector.testWeights`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute `tools:ignore="Orientation"` on the
  problematic XML element (or one of its enclosing elements). You may
  also need to add the following namespace declaration on the root
  element in the XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;LinearLayout xmlns:tools="http://schemas.android.com/tools"
      tools:ignore="Orientation" ...&gt;
    ...
  &lt;/LinearLayout&gt;
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="Orientation" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'Orientation'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore Orientation ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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